The invention pertains generally to the art of heat pumps and particularly to the art of grille and coil arrangements for the outdoor unit for a heat pump.
A typical heat pump of the air-to-air type for residential use, for example, includes an indoor coil unit in the air flow system of the residence, and an outdoor coil unit which ordinarily includes a coil per se, along with a refrigerant compressor and various control elements. When the heat pump is operating in a cooling mode the indoor coil functions as an evaporator and the outdoor coil as a refrigerant condenser. When the heat pump is reversed in its operation to a cooling mode, the indoor coil functions as a refrigerant condenser while the outdoor coil functions as a refrigerant evaporator. Consequently, there will be periods when the outdoor coil must be defrosted.
Most outdoor coil units have a coil which is disposed vertically and which has a protective openwork grille of one kind or another closely adjacent the exterior face of the coil. This grille may consist of horizontal and vertical welded wires, for example, or in some cases may be of an expanded metal type of construction. When the coil accumulates frost on it and requires defrost, it will frequently be found that the frost has built out onto the grille, so that a satisfactory defrost should result in all of the frost being removed from the grille as well as from the coil itself. The close adjacency of the grille to the face of the coil tends to retain the frost and ice on the face of the coil rather than letting it fall freely off. In other words, that ice and frost which is loosened at an upper level and would tend to fall freely but for the grille may be retained by lower level horizontal wires of the grille. Also, during freezing rain storms, ice and rain which falls from one horizontal wire tends to be caught by one or more of the lower horizontal wires.
One known way to avoid this problem is to space the grille means outwardly from the outer face of the coil a sufficient distance that the ice and frost does not bridge between the coil and grille. Accordingly during defrost the ice and frost is permitted to fall off the coil without any retention by the grille. However, this requires that the unit be larger than if that spacing did not need to be accommodated.
It is an aim of this invention to provide an arrangement in which the grille does not impede ice dropoff during defrost, and in which no penalty with respect to size of the overall unit is imposed.